1. Field of the Invention
This invention relates to an artificial joint device and a parallel linkage, which are applied to an artificial limb, such as a prosthetic limb or a limb of a robot.
2. Description of the Prior Art
Conventionally, an artificial joint device of the above-mentioned kind has been disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 11-345. The artificial joint device is applied to an ankle joint for connecting between a foot portion of an artificial leg and a leg portion of the same. The foot portion of the artificial leg has an upper end portion thereof formed with a through hole extending laterally. On the other hand, the leg portion of the artificial leg has a lower end thereof bifurcated into two arms to form a bracket with each arm having a hole formed therethrough at a location corresponding to an opening of the through hole extending laterally through the foot portion. In this artificial joint device, a shaft is fitted through the holes of the bracket and the through hole of the foot portion, which are aligned with each other, whereby the foot portion and the leg portion are capable of performing pivotal motion with respect to each other about a horizontal axis, only in the front-rear direction.
According to the above conventional artificial joint device, since the foot portion and the leg portion are allowed to perform pivotal motion with respect to each other about the horizontal axis, only in the front-rear direction, even when a person wearing the artificial leg tries to turn left or right while walking, the ankle joint portion cannot be twisted, which makes the turning motion difficult to perform. A combination of a serial linkage having three or more degrees of freedom and electric motors, used as a joint portion of a limb of a robot, is known as an artificial joint device capable of performing the twisting motion. However, this kind of artificial joint device needs at least three electric motors so as to ensure the three or more degrees of freedom and at the same time support the weight of the components of the robot. This increases the size of a power supply and that of the whole device, resulting in increased manufacturing costs of the device. Further, the increased device size and the necessity of the power supply make it difficult to apply the device to a prosthetic limb.